Transformer



July 26, 1932.

-S. E. ANDERSQN TRANSFORMER Original Filed Dec. 24, 1923 WAVE LENG 77! [I /IVE LENGTH 5. EAzvasnsoN ,4 TTDRNE),

Patented July 26, 1932 UNITED STATES,

PATENT OFFICE SIDNEY E. ANDERSON, OF MAPLEWOOD, NEW JERSEY, ASSIGN OR TO WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK v TRANSFORMER Original application filed December 24, 1823, Serial No. 682,418.

Patent No. 1,743,701, dated January'14,

1930. Divided and this applicationv filed August 24, 1929. Serial No. 388,058.

Th s is a division of my application Serial No. 682,418, filed December 24, 1923, re-

newed March 16, 1929, for vacuum tube circuits on which U. S. Patent No. 1,743,701 was granted January 14, 1930.

prises two vacuum tubes connected in pushpull or parallel-opposed relation with respect to the incoming circuit and in which subsequent stages each comprises a single vacuum tube amplifier. Among the advantages of this type of circuit are that the singing tendency is reduced and that the wave length range over which substantially uniform amplification is obtained is considerably increased over the case where a single tube is used in each stage; This latter effect is secured by providing individual couplings, such as transformers, between the respective tubes of the push-pull circuit and the succeed ng stage and by designing these transformers so that they have different and overlapping frequency transmission characteristics.

A more specific object of the present invention is to provide an improved radio receiving circuit of the general type disclosed in the Griffin patent referred to. l

A feature comprises an improved form of inter-stage coupling between the initial or push-pull stage and the succeeding stages to secure a more uniform transmission throughout a wide wave length range. Specifically, this latter feature comprises a three-winding transformer and a particular manner of connecting the windings of this transformer in the circuit to secure the most eflicient results in accordance with applicants discovery.

These tubes 17 and 18 are connected in paral- The exact nature of the invention and the i 4 various objects and features will appear more fully from the following detailed description of the invention 'asembodied intypical radio receiving circuits shown in the drawing.

Fig.1 is a schematic circuit diagram of a radio receiving circuit of one form which the invention may take; Figs. 2 and 3 illustrate different modes of connection of the transformer windings between the push-pull stage and the succeeding stage; Fig. 4 isfa View in section'of one form which the threewinding inter-stage transformer may take; and Fig. 5 shows curves illustrative of the effects of the different manners of connection illustrated in Figs. 2 and 3.

Referring first to Fig. 1, the receiving antenna is provided with the usual tuning condenser and with the inductance 11, which may be coupled, preferably variably, with the secondary inductances 12 and 13. When the switches 14 and 15 are closed, the second ary tuning condenser 15 is connected across the secondaries 12 and 13, these having interposed between them the fixed condensers 16, which are preferably of large enough capacity not to influence the tuning of the second ary circuit to any great extent.

The outer terminals of the secondaries 12 and 13 are connected to the grids of the respective vacuum tubes 17 and 18, which may be of the well known three-element type including a cathode, an anode and a suitable type of control element, such as the grid.

lei-opposed or push-pull relation with respect to the incoming circuit 10, 11 and serve to amplify the received radio frequency waves. The tubes 17 and 18 have included in their respective anode circuits individual primary windings 19 and 20, respectively, both of which are coupled to the common secondary 21 in the grid circuit of the second stage amplifier 22. Any number of succeeding stages of radio frequency amplification may be employed in addition to the amplifier 22. For the sake of simplicity, how.- ever, only one such succeeding stage is shown, this being coupled to the detector 23 by means of a second radio frequency transformer 24.

The detector 23 is provided with the usual grid leak and condenser arrangement shown, and includes in its output circuit a receiver R of any suitable type, such as a head set or a loud speaking receiver.

Space current is supplied to all of the tubes from the common source 28.

The filamentary cathodes of all of the tubes are connected in series with each other and the filament heating source 25, the negative pole of which is connected to earth. This heating circuit may be traced from the grounded pole of battery 25, first through the filament of the detector 23, then through the filament of the second stage amplifier 22, then through the filament of the tube 17, and finally through the filament of the tube 18 to the positive pole of the battery 25.

In order that the tubes 17 and 18 may operate properly in a balanced amplifier circuit, it is necessary that the grid of each tube have the proper normal potential relations with its own filament, and in general, the same potential with respect to its filament. The proper grid polarization for these tubes is obtained in accordance with the invention by connecting the grids to the proper points in the series filament heating circuit. For example, it will be seen that the grid of the tube 17 is connected to the more negative terminal of the filament of tube 22, which filament is included in the series filament heating circuit, next to the filament of the tube 17 in the direction of the negative pole of the filament heating battery. The grid of the tube 17 is therefore polarized more negative than the negative end of its cathode by the amount of potential drop in the filament of tube 22. Similarly, the grid of the tube 18 is connected to the more negative end of the filament of tube 17 which filament is included between the negative pole of bat ery 25 and the filament of tube 18 and is next adjacent the filament of tube 18 in the filament heating circuit. The grid of the tube 18 therefore possesses a polarizing potential which is more negative than the negative end of its own filament by the amount of the potential drop through the filament of the tube 17. Since tubes may readily be selected which have substantially the same filament resistance, the polarization of the grids of tubes 17 and 18 may, by the circuit arrangement just described, be made for all practical purposes equal.

The grid of the amplifier 22 may in a similar manner he polarized more negatively than its own filament by connecting it. as shown, to the more negative end of the filament of tube 23. r

This mode of connection of the filament in series is of particular advantage in the case of tubes using low voltage filaments, such as the Well known dry cell tubes. Such tubes require only small energy to heat the filaments. It is advantageous to connect their filaments in series since dry cells do not operate well in parallel on account of their having diiferent characteristics.

When the series type of filament heating circuit is to be used, a difficulty arises in the manner of impressing the received waves upon the grids of the push-pull tubes and of tuning the grid circuits of these tubes to the wave length to be received. In the case where the filaments are connected in parallel, as in the Griifin patent above referred to, the filaments of the push-pull tubes are at the same potential, and a connection may therefore be made from the common filament circuit of these tubes to the mid-point of the secondary of the input transformer. filament heating circuit is employed, however, independent conductive circuits must be maintained between each grid and a difierent point of the filament heating circuit so that a different mode of impressing the waves on the grids must be adopted. In accordance with the invention, individual alternating current paths are provided from each grid through one or the other of the secondary inductances 12 or 13 and one or the other of the condensers 16 to a common point in the circuit, such as ground. Since the cathodes are also connected to ground, the alternating current potentials impressed on the two grids may be made equal by this form of connection.

In order to make use of the push-pull cir'- cuit to secure a broader characteristic for the amplifier, it is necessary, as pointed out above, to provide transmission paths between the individual tubes 17 and 18 and the second stage tube 22, which paths have respectively different transmission characteristics. This may be done, as in the Griflin patent referred to, by providing two separate transformers between these two stages. It has been found, however, in practice, that in some cases the use of two separate transformers introduces difiiculties, the causes of which are not thoroughly understood, but which may be due to different phase relations existing between the waves in the two transformers so that in one region of the wave length range a different resultant effect is obtained from that which exists in a different region of the wave length range. Such difiiculties have been overcome in accordance with the invention by providing a three-winding transformer comprising the primary windings 19 and 20 and the common secondary winding 21.

The manner of constructing this transformer is best illustrated in Fig. l, to which reference will now be made. The spool 26, preferably of insulating material, has cut w into it three parallel, concentric annular grooves, in which the windings are placed.

These grooves have relatively great depth When the series compared with their width. In one instance, the spool had an external diameter of the order of 2 inches, each groove was of the order of inch deep and of 1% of an inch, or preferably less, in width. No attempt has been made in Fig. 4 to employ a scale to denote the preferred relative dimensions. In Fig. 4, the preferred positions of the windings 19, 20 and 21 are indicated. The spacing between the respective windings and the number of turns in each winding may be varied depending on the wave lengths to be transmitted, the design of the tube used, etc, and in general it will be found that by using different number of turns in the two windings 19 and 20 and by properly relating these windings to the common secondary 21, the amplifier will be given a much broader wave length characteristic than as though the windings 19 and 20 had each the same number of turns. The proper number of turns to be used in an initial case may be determined by a cut-and-try method, and it will in general be readily observed whether a given change in the number of turns improves the characteristic in the desired direction or not, so that by a few successive tries, with the previous knowledge that the number of turns in the windings 19 and 20 should be different, the desired transmission characteristic will be secured.

It has been found that the transmission characteristic depends not only upon the dimensions of the three-Winding transformer, both the mechanical and electrical, but also upon the manner of connecting it into the circuit.

The effect of the difi'erent modes of connection is shown in Figs. 2, 3 and 5. In Fig. 2, the anode of the tube 17 is connected to the outer terminal of the winding 19, this terminal being indicated in Figs. 2 and 4 as 0. The anode of the tube 18 is connected to the inner terminal of the winding 20, this being indicated in Figs. 2 and 1 by i. The other terminals of the windings 19 and 20 are connected together and through the plate battery to the filament circuit. The inner terminal of the winding 21 is connected to the grid of the tube 22 and the outer terminal is connected to the filament circuit. With this type of connection it is found that a characteristic of relatively narrow wave length range and with the highest amplification at the central portion only is obtained. This is indicated by the curve I of Fig. 5. It is, of course, immaterial whether the plate of the tube 17 is connected to the outer terminal of the winding 19 or whether the plate of the tube 18 is connected to the outer terminal of the winding 20 so long as the plates of the respective tubes are connected to respectively opposite terminals, that is, one to the outer and the other to the inner. It is also immaterial whether the grid of the tube 22 is consuch as is shown by the curve II of Fig. 5,is

obtained. No explanation of this effect is attempted here except that it is probably due to the capacity relations between the different windings, it being known that at the relatively short wave lengths the capacity effects between different portions of the circuit have considerable influence on the transmissio characteristics.

In reversing the terminal connections of a winding in this manner, it is of course necessary that the direction of the winding itself be also reversed to avoid the output of one of the tubes 17 opposing that of the other tube in its effect in transmitting waves to the com mon secondary.

The transformer 24 preferably has a wavelength gain characteristic such that it cooperates with the transformer 19, 20, 21 to give substantially uniform transmission over a wave-length range as broad as the characteristic of the transformer 19, 20, 21 alone. This may result, for example, from the transformer 24: having its highest gain displaced in the wave-length range from the point or points of highest gain of amplifier 19, 20, 21 so that the combined effect of the two transformers in giving uniform transmission is superior to either alone.

It is to be understood that the invention is not to be limited to any particular wave length region nor to any of the values or di m-ensions that have been given, nor to the specific circuit arrangements that have been described and shown in detail, but only by the scope of the appended claims.

What is claimed is:

1. A radio frequency transformer having a primary winding and a secondary winding, said secondary winding comprising a coil of disc shape having a large depth compared with its width of winding, said primary winding comprising two coils symmetrically located with respect to said secondary winding, said primary windings being wound in opposite directions and having one end of one of said coils of said primary winding connected to the closest end of the other of said J coils of said primary winding.

2. A radio frequency transformer comprising a winding having an intermediate point and another winding in electromagnetic inductive relation thereto, the turns on either side of the intermediate point of said windin-ghaving an intermediate point so positioned in relation to each successive turn of the said other winding in electromagnetic inductive relation thereto that when the said transformer is energized the electrostatic flux emanating from either winding induces electrostatic charges between said turns on one side of said intermediate point of said winding having an intermediate point and said other winding of opposite polarity to the electrostatic charges induced between said turns on the other side of said intermediate point and said other winding, thereby causing a reduction in the difference of potential between the extremities of'the said other winding due to said electrostatic charges, while the electromagnetic flux emanating from either Winding induces in the other winding electromotive forces which are cu mulative.

In witness whereof, I hereunto sub-scribe my name this 22d day of August, 1929.

SIDNEY E. ANDERSON. 

